Eyewitnesses can speak in third person. Consider Bob Dole, who always spoke of himself as "Bob Dole" and not "I." Moses wrote Exodus, Leviticus, Numbers, and Deuteronomy as an eyewitness. New Testament writers confirm that Moses wrote these books, yet he speaks of himself in third person. In the culture of the Twentieth and Twenty-first century writers may prefer first person, but that policy does not necessarily pertain in other cultures.
Personally, I am not sure that Adam or Noah wrote anything down. Adam told Methuselah, Methuselah told Shem, and Shem told Abraham, with the confirming testimony of their own sons and grandchildren, verifying that the the account was being related accurately. Then as life spans became shorter and memories more defective, the record was written down. Moses wrote it down INFALLIBLY in the book of Genesis.
But since we believe that this Scripture is God-breathed, given through holy men of old who were borne along by the Holy Spirt, then we believe that it is God's Own EYE WITNESS record of what really did happen, before man was created and in the creation of the first two humans, Adam out of Dust, and Eve out of the side of Adam.